1. Field of the Invention
This invention relates to a semiconductor laser, and more particularly to a semiconductor laser in which the temperature of a laser diode chip is controlled by a Peltier element through a heat radiating plate.
2. Description of the Related Art
There have been provided various types of semiconductor lasers. In many of them, a laser diode chip is enclosed in a package and a laser beam emitted from the laser diode chip emanates outside the package through a glass window.
In those of high output types out of such semiconductor lasers, the laser diode chip is mounted on a heat radiating plate and the heat radiating plate is mounted on a Peltier element, and the temperature of the laser diode chip is controlled constant by a temperature detecting means and a temperature control circuit such as the Peltier element and a thermistor.
The cooling surface of the Peltier element is generally formed of alumina. Accordingly the heat radiating plate is also formed of alumina so that the Peltier element and the heat radiating plate are not strained due to change in temperature.
In the conventional semiconductor laser where the temperature of the laser diode chip is controlled constant in the manner described above, there has been a problem that the cooling capacity of the Peltier element is small. For example, in a semiconductor laser of output power of 2 W, the cooling limit temperature under an environmental temperature of 45.degree. C. is rather high and 25 to 30.degree. C. When the cooling capacity of the Peltier element is small, the working wavelength range of the semiconductor laser is limited and/or the service life of the semiconductor laser is shortened.